Various surfaces, particularly metal surfaces, require a protective coating especially when the surface will be prone to corrosive environment exposure. Metal surfaces for use in a wide variety of industries, for example, automotive, agricultural, aircraft, construction, and industrial, are particularly prone to corrosion and require protection against corrosive environments. It is important therefore that coatings for metal surfaces are resistant to various chemicals, water, and the weather. It is equally important that these coatings have excellent adhesion characteristics.
Metal surfaces have traditionally been coated with high performance two-component protective coating compositions consisting of an epoxy primer and a polyurethane topcoat. The epoxy primers are used to provide adherence to the metal surface and to adhere to the topcoat while preventing corrosion. However, most conventional two-component primer compositions have shown lack luster adhesion and corrosion resistance performance, particularly when used on refinished surfaces or metals surfaces treated with a zinc containing material (e.g., galvanized). Refinished metal surfaces are generally those which have undergone sanding or grinding, which typically results in the bare metal surface being exposed. Examples of commonly encountered refinished metal surfaces include metal aluminum, galvanized steel, and cold rolled steel. Bare metal is often exposed as a result of the removal of the previously applied coating layers containing and/or surrounding the defect area. It is often difficult to obtain adequate adhesion of coatings applied directly to exposed metal surfaces and exposed refinished metal surfaces.
Accordingly, there exists a need in the art for an improved coating compositions having improved adhesion to metal surfaces (including galvanized metal surfaces and bare metal surfaces), corrosion resistance, exterior weathering durability, and water/humidity resistance.